Sorgun linyit-su karışımının iyonik olmayan bir dispersant ile hazırlanması ve incelenmesi
Başlık çevirisi mevcut değil.
- Tez No: 75196
- Danışmanlar: YRD. DOÇ. DR. REHA YAVUZ
- Tez Türü: Yüksek Lisans
- Konular: Kimya Mühendisliği, Chemical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1998
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Kimya Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 120
Özet
ÖZET Toplam rezervi 8 milyar ton olan ve ülkemiz fosil enerji kaynaklan içinde birinci sırada yer alan linyit kömürü hem günümüzde hem de yakın gelecekte vazgeçemeyeceğimiz bir enerji kaynağı durumundadır. Fakat Türk linyitlerinin yumuşak karakterde olması nedeniyle, üretimleri, hazırlanmaları, taşınmaları ve depolanmaları sırasında çok miktarda toz kömür oluşumu söz konusudur. Bu nedenle yurdumuzdaki kömür işletmelerinin çoğunda değerlendirilemeyen toz kömür stokları vardır. Bu stoklarda meydana gelen kendiliğinden tutuşma olayları büyük sorunlar yaratmakta ve hava kirliliğine neden olmaktadır. Ayrıca, yağmur sulan ile sürüklenen toz kömürler ile suda çözünen çeşitli maddeler çevre sularının kirlenmesine yol açmaktadır. Enerji tüketiminin hızla arttığı günümüz koşullarında, yenilenemeyen bir enerji kaynağı olan linyitlerimizin en iyi şekilde değerlendirilmesi gerekmektedir. Kömür tozlarının değerlendirilmesi amacıyla geliştirilmiş ve uygulanmakta olan en önemli yöntemlerden birisi kömür-sıvı karışımları (KSK) halinde yakılmasıdır. KSK yakıtında çeşitli kimyasal katkı maddeleri farklı amaçlarla kullanılmaktadır. Bunlar; kömürün ıslanmasını sağlayan maddeler, kömürün su içinde dağılmasını sağlayan dağıtıcı maddeler ve çökelmeyi önleyici katkı maddeleri olarak özetlenebilir. Bu çalışmanın temel amacı, Yozgat- S orgun linyit numunesi kullanılarak uygun linyit- su karışımının hazırlanması ve viskozite özelliklerinin belirlenmesidir. Bu amaçla, öncelikle kömür-su karışımlarının hazırlanmasında uygun olduğu belirtilen iyonik olmayan bir dispersantın (Tween-80; polioksietilen sorbitan monooleat), Yozgat- Sorgun linyit numunesiyle olan adsorpsiyon davranımı incelenmiştir. Dispersant adsorpsiyonunu, ortamdaki iyonik bir ıslatıcı madde (Texapon N25; sodyum loril eter sülfat) varlığının ne şekilde etkilediği belirli bir sıcaklık için (293 K) farklı pH değerlerinde (pH=5, pH=7 ve pH=9), farklı dispersant miktarları kullanılarak incelenmiştir. Belirli bir dispersant oranı için, sıcaklık (278 K, 293 K ve 303 K) ve pH'ın (pH=5, pH=7 ve pH=9) adsorpsiyon davranımını ne şekilde etkilediği araştırılmıştır. Adsorpsiyon deneyleri ağırlıkça %20'lik linyit-su karışımı esas alınarak gerçekleştirilmiştir. Linyit derişiminin dispersant adsorpsiyonuna etkisi, 293 K sıcaklık, pH=5 ve 2 saatlik dispersant adsorpsiyon süresi esas alınarak incelenmiştir. Daha sonra farklı pH, sıcaklık ve dispersant oranlarının linyit-su karışımının viskozitesine etkisi belirlenmiştir. Sonuç olarak, Tween-80 dispersantının Yozgat- Sorgun linyit numunesi ile olan adsorpsiyon davranımı incelenerek, adsorpsiyonun en iyi olduğu koşullar saptanmış ve linyit-su karışımının belirli koşullardaki viskoziteleri belirlenmiştir. xı
Özet (Çeviri)
SUMMARY PREPARATION AND INVESTIGATION OF SORGUN LIGNITE-WATER SLURRY WITH A NON-IONIC DISPERSANT Lignite is an important energy source of Turkey. Large amount of fine lignite particles form during cleaning and mining processes in Turkey because of the soft characteristics of Turkish lignites. These fine lignite particles cannot be easily handled, stored and transported. These particles can also cause some environmental problems, such as air and water pollution. Therefore, it is important to solve these problems by using fine lignite particles as efficient as possible. Three methods to process fine coal particles are widely used. These are: a) Combustion in pulverized coal combustion systems, b) Briquetting and c) Using in the preparation of coal-liquid fiaels. Consumption of petroleum based fuels can be reduced substantially or replaced completely with coal slurry fuel. Such slurry fuels are a particularly attractive alternative liquid fuel for large stationary power systems and liquid fuel fired appliances. Research on the coal slurry fuels began with the preparation of coal-oil mixtures nearly a century ago. But, coal-oil mixture combustion is not viewed as the long term solution to the energy crisis. Using water as the liquefying media was considered to eliminate the consumption of petroleum based fuels. Thus, studies on preparation and combustion of coal-water slurries (CWSs) became popular. One of the major advantages of the CWS is to eliminate completely all the oil consumption by converting to coal without the complicated and expensive techniques of liquefaction or gasification. CWSs are primaryly considered as a replacement for fuel oil in retrofit applications, but they may also be the future clean fuel for new coal- fired plants. CWSs may also have a future as a fuel for gas turbines and diesel engines, fluidized bed combustors and dryers, blast furnaces, and gasification systems. CWS is typically composed of 60-75% coal, 24-39% water, and 1% chemical additives (unless otherwise noted, all percentages are by weight). The physical and combustion characteristics of the CWS vary depending on the following factors: 1. The type of coal used in the preparation of the CWS, XII2. Coal size, shape, and particle size distribution, 3. The quality of inorganic material in the coal after sizing and cleaning, 4. The solid content of the mixture, 5. The stability of the fuel, and 6. The chemical additives present to modify the viscosity and stability of the mixture. These factors influence the fuel transportation, storage, and flow properties, the atomization and flame characteristics, the energy density, and the emissions; they must be considered when developing a suitable fuel specification. Surfactaints are generally described as anionic, non-ionic, cationic or amphoteric. Most industrial and domestic processes using chemicals involve contact between a liquid and a solid where the solid needs wetting. This is exactly the function of the surfactant. However, there are many products which can easily wet substrates better than water, for example alcohol, hydrocarbons, etc. It is the particular property of surfactants to decrease the surface tension of water using very low concentrations. The hydrophobic group for 99% of surfactants is made up of hydrocarbon chains and the majority of these are linear due to the demands for biodegradability. The hydrophobic group will constitute the largest part of the molecule except for high ethylene oxide non-ionics and thus is the major cost of a surfactant molecule. The hydrophobic group based on hydrocarbons is basically available from three sources: Petrochemicals, natural vegetable oils and natural animal fats. The principal properties which characterize surfactants are described:. Adsorption. Surface tension and interfacial tension. Micelles. Wetting of solids. Dispersing /aggregation of solids. Foaming /defoaming. Emulsifying /demulsifying There are two basic concepts which need to be well understood in order to explain the majority of observed phenomena: these are adsorption of a surfactant at a surface and the formation of micelles in solution. These two phenomena differentiate a surfactant from other chemical entities. It is adsorption at surfaces which gives the surface active effects of foaming, wetting, emulsification, dispersing of solids and detergency. It is the micelle properties which give the solution and bulk properties of surfactants such as viscosity and solubility. XlllAdsorption of surfactant on solid surfaces will depend upon the nature of the surface, whether hydrophilic (polar) or hydrophobic (non-polar). Polar or hydrophilic surfaces; 1. The chemical nature of the surface can play an important role, e.g. metal oxides can form salts on the surface (chemisorption) with anionics. 2. With polar surfactants, adsorption can be high; the polar groups can orient towards the surface and the hydrophobic chain then makes the particle hydrophobic. A second layer can be formed with hydrophilic groups on the outside. Non-polar or hydrophobic surfaces; 1. The amount of adsorption is extremely small with polar surfactants. 2. The adsorption of polar surfactants can be increased by addition of electrolytes which reduces the electrical double layer., I 3. Non-ionics adsorb in appreciably higher amounts (10 x) than polar surfactants. 4. Electrolyte addition does not significantly affect the amount of adsorption of non- ionics. 5. Effect of temperature: polar surfactants adsorb less with increase in temperature. Adsorption of ethoxylates increase with increasing temperature (because they hydrated as the temperature is increased thereby becoming more hydrophobic). 6. Increase in the length of the hydrocarbon chain increases adsorption. 7. Branching in the hydrocarbon chain decreases adsorption. If further surfactant is added to the solution, the surfactant molecules remain in the bulk of the solution but these hydrophobic heads will still be repelled from the water. They can form spherical assemblies known as micelles where the interior of the micelle resembles a separate hydrocarbon phase. The concentration at which micelles first form is known as the critical micelle concentration (CMC). These micelles behave as large molecules and influence two important properties: 1. Solubility of organic hydrocarbons and oils in aqueous solution and 2. Viscosity The size of micelle is measured by the aggregation number which is the number of surfactant molecules associated with a micelle. Surfactant solutions with spherical micelles behave like Newtonian liquids, i.e. the viscosity is independent of shear rate and not very different from water. The transition from spherical to cylindrical or lamellar micelles results in a large viscosity xivincrease which changes the solution to non-Newtonian, i.e. dependent upon shear rate. Non-ionic surfactants are surfactants which do not have a charged group. The hydrophilic group is provided by a water soluble group which does not ionise. The most common are the hydroxyl group (R-OH) and the ether group (R-O-R'). Other groups are the oxide groups such as those in amine oxide and the triple unsaturated bonds such as those in acetylenic alcohols. The solubility of ethylene oxide (EO) derivatives is due to the hydrogen bond between water and the EO group. Energy of hydrogen bond is approx. 29.29 kJ/mol and heating can impart enough energy to destroy the bond. Dehydration takes place and the product comes out of solution; the temperature at which this takes place is known as the cloud point. The water solubility increases as the amount of ethylene oxide increases. There is a simple rule of thumb relating the amount of ethylene oxide with the number of carbon atoms (N) in the hydrophobe to achieve water solubility; water solubility just achieved at N/3 moles of EO; fairly good water.solubility at N/2 moles of EO; \fery good water solubility at 3 N/2 moles of EO. Non-ionics tend to have maximum surface activity near the cloud point. Addition of alkalis and/or inorganic salts generally lowers the cloud point but there is no consistent pattern on the addition of inorganic acids. Addition of large quantities of inorganic salts can cause precipitation at room temperature (salting out). One advantage of the non-ionic surfactants is that they are compatible with ionic and amphoteric surfactants. Polyoxyethylene solubilization is the key to the substantial and continuing growth of the non-ionic surfactants. In this study, preparation and viscosity of lignite-water slurry (LWS) of Yozgat- Sorgun lignite were investigated. Adsorption behaviour of a non-ionic (polyoxyethylene sorbitan monooleate; Tween-80) type dispersant, which is widely used in the preparation of coal-water slurries in the literature, on Yozgat-Sorgun lignite sample was investigated. The effect of an ionic (sodium lauryl ether sulphate; Texapon N25) type wetting agent on dispersant adsorption was studied by changing the concentration of dispersant at three different pH values (pH=5, 7 and 9) at constant temperature (293 K). Results can be summarized briefly as follows. Dispersant adsorption was strongly affected by the pH value. LWS of Yozgat- Sorgun lignite sample showed the best adsorption behaviour at neutral pH. The effect of temperature on dispersant adsorption was studied at 278 K, 293 K and 303 K. Dispersant adsorption of Tween-80 was increased when the temperature increased from 278 K to 303 K. The effect of LWS concentration on dispersant adsorption was investigated by stirring 2 hours at 293 K and at pH=5. It was observed that increasing the LWS concentration decreased the dispersant adsorption efficiency of Tween-80. xvThe viscosity of Yozgat-Sorgun LWS prepared under different conditions was determined using a rotational rheometer (Mertler, Rheomat RM-180S). It was found that the viscosities of LWSs were strongly affected by the pH value, temperature, LWS concentration and the chemical additives which were Tween-80 and Texapon N25. The results observed on the viscosity of LWS can be summarized as follows: Viscosity of LWS decreased when the temperature was increased from 283 K to 303 K. In addition, viscosity of LWS was decreased because of the thixotropic behaviour. Therefore; viscosity decrease is dependent on both temperature and thixotropic behaviour of LWS at high temperature. Viscosity of LWS was found to be low at pH=9, however to be high at pH=7. Using Texapon N25 in the preparation of LWS decreased viscosity of LWS. This effect is more evident at high temperature. ? i Increasing the LWS concentration increased the viscosity of the slurry. xvi
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